Several safety devices are disposed in an automobile with the aim of securing occupant safety. For example, an air bag module for deploying an air bag using gas generated by an inflator during an emergency, such as a collision, is one such safety device.
As shown in FIG. 7, a front passenger seat air bag module, which is one type of air bag module, is housed in an air bag case 2 such that a folded air bag 1 is covered by a strip-form flap 3 (Patent Document 1, for example).    Patent Document 1: Japanese Patent Application Publication No. 2007-62455
As shown in FIG. 8, this air bag module is attached by engaging a hook 2b, which is attached to the vicinity of an opening in one side wall 2a of the air bag case 2, with an engagement hole 4aa in an upright wall 4a provided on an inner side of an instrument panel 4. Note that a reference numeral 5 in FIG. 8 denotes an inflator.
Incidentally, in this air bag module, the entire periphery of the air bag is covered by a box-shaped metal or resin air bag case having an open ceiling surface in order to maintain the folded shape of the air bag during installation in a vehicle and restrict a deployment direction during deployment.
However, this air bag case is heavy, which runs counter to recent trends toward weight reduction. Further, the air bag case requires a large amount of resources, which runs counter to recent trends toward resource conservation. Moreover, the strength of an attachment portion of the air bag module must be increased in accordance with the increased weight of the air bag case.
A problem to be solved by the present invention is that when a conventional metal or resin box-shaped air bag case is employed, an increase in the amount of required resources and an increase in weight occur, and therefore resource saving and weight reduction cannot be achieved. Moreover, the strength of the attachment portion of the air bag module must be increased in accordance with the increase in weight.